2 * Hook output functions (like printf(3)) with LD_PRELOAD to color stderr (or
3 * other file descriptors).
5 * Copyright (C) 2013 Simon Ruderich
7 * This program is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program. If not, see <http://www.gnu.org/licenses/>.
25 /* Must be loaded before the following headers. */
26 #include "ldpreload.h"
28 /* Disable assert()s if not compiled with --enable-debug. */
48 #ifdef HAVE_STRUCT__IO_FILE__FILENO
52 /* The following functions may be macros. Undefine them or they cause build
53 * failures when used in our hook macros below. */
55 /* In glibc, real fwrite_unlocked() is called in macro. */
56 #undef fwrite_unlocked
57 /* In Clang when compiling with hardening flags (fortify) on Debian Wheezy. */
62 /* Used by various functions, including debug(). */
63 static ssize_t (*real_write)(int, void const *, size_t);
64 static int (*real_close)(int);
65 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
67 /* Did we already (try to) parse the environment and setup the necessary
69 static int initialized;
70 /* Force hooked writes even when not writing to a tty. Used for tests. */
71 static int force_write_to_non_tty;
74 #include "constants.h"
79 #include "hookmacros.h"
84 /* See hookmacros.h for the decision if a function call is colored. */
87 /* Prevent inlining into hook functions because it may increase the number of
88 * spilled registers unnecessarily. As it's not called very often accept the
90 static int isatty_noinline(int fd) noinline;
91 static int isatty_noinline(int fd) {
94 int saved_errno = errno;
95 int result = isatty(fd);
102 static void dup_fd(int oldfd, int newfd) {
104 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
107 assert(oldfd >= 0 && newfd >= 0);
109 if (unlikely(!initialized)) {
110 init_from_environment();
113 /* We are already tracking this file descriptor, add newfd to the list as
114 * it will reference the same descriptor. */
115 if (tracked_fds_find(oldfd)) {
116 if (!tracked_fds_find(newfd)) {
117 tracked_fds_add(newfd);
119 /* We are not tracking this file descriptor, remove newfd from the list
122 tracked_fds_remove(newfd);
126 static void close_fd(int fd) {
128 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
133 if (unlikely(!initialized)) {
134 init_from_environment();
137 tracked_fds_remove(fd);
141 /* "Action" handlers called when a file descriptor is matched. */
143 static char const *pre_string;
144 static size_t pre_string_size;
145 static char const *post_string;
146 static size_t post_string_size;
148 /* Load alternative pre/post strings from the environment if available, fall
149 * back to default values. */
150 static void init_pre_post_string(void) {
151 pre_string = getenv(ENV_NAME_PRE_STRING);
153 pre_string = DEFAULT_PRE_STRING;
155 pre_string_size = strlen(pre_string);
157 post_string = getenv(ENV_NAME_POST_STRING);
159 post_string = DEFAULT_POST_STRING;
161 post_string_size = strlen(post_string);
164 /* Don't inline any of the pre/post functions. Keep the hook function as small
165 * as possible for speed reasons. */
166 static void handle_fd_pre(int fd) noinline;
167 static void handle_fd_post(int fd) noinline;
168 static void handle_file_pre(FILE *stream) noinline;
169 static void handle_file_post(FILE *stream) noinline;
171 static void handle_fd_pre(int fd) {
172 int saved_errno = errno;
174 if (unlikely(!pre_string || !post_string)) {
175 init_pre_post_string();
178 DLSYM_FUNCTION(real_write, "write");
179 real_write(fd, pre_string, pre_string_size);
183 static void handle_fd_post(int fd) {
184 int saved_errno = errno;
186 /* write() already loaded above in handle_fd_pre(). */
187 real_write(fd, post_string, post_string_size);
192 static void handle_file_pre(FILE *stream) {
193 int saved_errno = errno;
195 if (unlikely(!pre_string || !post_string)) {
196 init_pre_post_string();
199 DLSYM_FUNCTION(real_fwrite, "fwrite");
200 real_fwrite(pre_string, pre_string_size, 1, stream);
204 static void handle_file_post(FILE *stream) {
205 int saved_errno = errno;
207 /* fwrite() already loaded above in handle_file_pre(). */
208 real_fwrite(post_string, post_string_size, 1, stream);
215 /* Hook all important output functions to manipulate their output. */
217 HOOK_FD3(ssize_t, write, fd,
218 int, fd, void const *, buf, size_t, count)
219 HOOK_FILE4(size_t, fwrite, stream,
220 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
223 HOOK_FILE2(int, fputs, stream,
224 char const *, s, FILE *, stream)
225 HOOK_FILE2(int, fputc, stream,
226 int, c, FILE *, stream)
227 HOOK_FILE2(int, putc, stream,
228 int, c, FILE *, stream)
229 HOOK_FILE1(int, putchar, stdout,
231 HOOK_FILE1(int, puts, stdout,
234 /* printf(3), excluding all s*() and vs*() functions (no output) */
235 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
236 char const *, format)
237 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
238 FILE *, stream, char const *, format)
239 HOOK_FILE2(int, vprintf, stdout,
240 char const *, format, va_list, ap)
241 HOOK_FILE3(int, vfprintf, stream,
242 FILE *, stream, char const *, format, va_list, ap)
243 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
244 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
245 int, flag, char const *, format)
246 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
247 FILE *, fp, int, flag, char const *, format)
248 HOOK_FILE3(int, __vprintf_chk, stdout,
249 int, flag, char const *, format, va_list, ap)
250 HOOK_FILE4(int, __vfprintf_chk, stream,
251 FILE *, stream, int, flag, char const *, format, va_list, ap)
253 /* unlocked_stdio(3), only functions from above are hooked */
254 HOOK_FILE4(size_t, fwrite_unlocked, stream,
255 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
256 HOOK_FILE2(int, fputs_unlocked, stream,
257 char const *, s, FILE *, stream)
258 HOOK_FILE2(int, fputc_unlocked, stream,
259 int, c, FILE *, stream)
260 HOOK_FILE2(int, putc_unlocked, stream,
261 int, c, FILE *, stream)
262 HOOK_FILE1(int, putchar_unlocked, stdout,
264 /* glibc defines (_IO_)putc_unlocked() to a macro which either updates the
265 * output buffer or calls __overflow(). As this code is inlined we can't
266 * handle the first case, but if __overflow() is called we can color that
267 * part. As writes to stderr are never buffered, __overflow() is always called
268 * and everything works fine. This is only a problem if stdout is dupped to
269 * stderr (which shouldn't be the case too often). */
270 #ifdef HAVE_STRUCT__IO_FILE__FILENO
271 /* _IO_FILE is glibc's representation of FILE. */
272 HOOK_FD2(int, __overflow, f->_fileno, _IO_FILE *, f, int, ch)
276 HOOK_VOID1(void, perror, STDERR_FILENO,
279 /* err(3), non standard BSD extension */
281 HOOK_VAR_VOID2(void, err, STDERR_FILENO, verr,
282 int, eval, char const *, fmt)
283 HOOK_VAR_VOID2(void, errx, STDERR_FILENO, verrx,
284 int, eval, char const *, fmt)
285 HOOK_VAR_VOID1(void, warn, STDERR_FILENO, vwarn,
287 HOOK_VAR_VOID1(void, warnx, STDERR_FILENO, vwarnx,
289 HOOK_FUNC_SIMPLE3(void, verr, int, eval, const char *, fmt, va_list, args) {
290 /* Can't use verr() directly as it terminates the process which prevents
291 * the post string from being printed. */
295 HOOK_FUNC_SIMPLE3(void, verrx, int, eval, const char *, fmt, va_list, args) {
300 HOOK_VOID2(void, vwarn, STDERR_FILENO,
301 char const *, fmt, va_list, args)
302 HOOK_VOID2(void, vwarnx, STDERR_FILENO,
303 char const *, fmt, va_list, args)
306 /* error(3), non-standard GNU extension */
308 static void error_vararg(int status, int errnum,
309 char const *filename, unsigned int linenum,
310 char const *format, va_list ap) {
311 static char const *last_filename;
312 static unsigned int last_linenum;
314 /* Skip this error message if requested and if there was already an error
315 * in the same file/line. */
316 if (error_one_per_line
317 && filename != NULL && linenum != 0
318 && filename == last_filename && linenum == last_linenum) {
321 last_filename = filename;
322 last_linenum = linenum;
324 error_message_count++;
328 if (error_print_progname) {
329 error_print_progname();
331 fprintf(stderr, "%s:", program_invocation_name);
333 if (filename != NULL && linenum != 0) {
334 fprintf(stderr, "%s:%u:", filename, linenum);
335 if (error_print_progname) {
336 fprintf(stderr, " ");
339 if (!error_print_progname) {
340 fprintf(stderr, " ");
344 vfprintf(stderr, format, ap);
347 fprintf(stderr, ": %s", strerror(errnum));
350 fprintf(stderr, "\n");
356 void error_at_line(int status, int errnum,
357 char const *filename, unsigned int linenum,
358 char const *format, ...) {
361 va_start(ap, format);
362 error_vararg(status, errnum, filename, linenum, format, ap);
365 void error(int status, int errnum, char const *format, ...) {
368 va_start(ap, format);
369 error_vararg(status, errnum, NULL, 0, format, ap);
375 /* Hook functions which duplicate file descriptors to track them. */
378 HOOK_FUNC_DEF1(int, dup, int, oldfd) {
381 DLSYM_FUNCTION(real_dup, "dup");
383 newfd = real_dup(oldfd);
385 dup_fd(oldfd, newfd);
390 /* int dup2(int, int) */
391 HOOK_FUNC_DEF2(int, dup2, int, oldfd, int, newfd) {
392 DLSYM_FUNCTION(real_dup2, "dup2");
394 newfd = real_dup2(oldfd, newfd);
396 dup_fd(oldfd, newfd);
401 /* int dup3(int, int, int) */
402 HOOK_FUNC_DEF3(int, dup3, int, oldfd, int, newfd, int, flags) {
403 DLSYM_FUNCTION(real_dup3, "dup3");
405 newfd = real_dup3(oldfd, newfd, flags);
407 dup_fd(oldfd, newfd);
413 /* int fcntl(int, int, ...) */
414 HOOK_FUNC_VAR_DEF2(int, fcntl, int, fd, int, cmd /*, ... */) {
418 DLSYM_FUNCTION(real_fcntl, "fcntl");
420 /* fcntl() takes different types of arguments depending on the cmd type
421 * (int, void and pointers are used at the moment). Handling these
422 * arguments for different systems and with possible changes in the future
425 * Therefore always retrieve a void-pointer from our arguments (even if it
426 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
427 * problems because a void-pointer is most-likely bigger than an int
428 * (something which is not true in reverse) and shouldn't cause
429 * truncation. For register based calling conventions an invalid register
430 * content is passed, but ignored by real_fcntl(). Not perfect, but should
434 result = real_fcntl(fd, cmd, va_arg(ap, void *));
437 /* We only care about duping fds. */
438 if (cmd == F_DUPFD && result != -1) {
446 HOOK_FUNC_DEF1(int, close, int, fd) {
447 DLSYM_FUNCTION(real_close, "close");
452 return real_close(fd);
454 /* int fclose(FILE *) */
455 HOOK_FUNC_DEF1(int, fclose, FILE *, fp) {
458 DLSYM_FUNCTION(real_fclose, "fclose");
460 if (fp != NULL && (fd = fileno(fp)) >= 0) {
463 return real_fclose(fp);
467 /* Hook functions which are necessary for correct tracking. */
469 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
471 /* vfork() is similar to fork() but the address space is shared between
472 * father and child. It's designed for fork()/exec() usage because it's
473 * faster than fork(). However according to the POSIX standard the "child"
474 * isn't allowed to perform any memory-modifications before the exec()
475 * (except the pid_t result variable of vfork()).
477 * As some programs don't adhere to the standard (e.g. the "child" closes
478 * or dups a descriptor before the exec()) and this breaks our tracking of
479 * file descriptors (e.g. it gets closed in the parent as well), we just
480 * fork() instead. This is in compliance with the POSIX standard and as
481 * most systems use copy-on-write anyway not a performance issue. */
487 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
488 * a custom environment which doesn't necessarily contain our updates to
489 * ENV_NAME_FDS. It's also faster to update the environment only when
490 * necessary, right before the exec() to pass it to the new process. */
492 /* int execve(char const *, char * const [], char * const []) */
493 HOOK_FUNC_DEF3(int, execve, char const *, filename, char * const *, argv, char * const *, env) {
494 DLSYM_FUNCTION(real_execve, "execve");
499 /* Count arguments and search for existing ENV_NAME_FDS environment
502 char * const *x = env;
504 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
512 /* Terminating NULL. */
515 char *env_copy[count + 1 /* space for our new entry if necessary */];
516 memcpy(env_copy, env, count * sizeof(char *));
518 /* Make sure the information from the environment is loaded. We can't just
519 * do nothing (like update_environment()) because the caller might pass a
520 * different environment which doesn't include any of our settings. */
522 init_from_environment();
525 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
526 strcpy(fds_env, ENV_NAME_FDS "=");
527 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
530 env_copy[index] = fds_env;
532 /* If the process removed ENV_NAME_FDS from the environment, re-add
534 env_copy[count-1] = fds_env;
535 env_copy[count] = NULL;
538 return real_execve(filename, argv, env_copy);
541 #define EXECL_COPY_VARARGS_START(args) \
545 /* Count arguments. */ \
546 size_t count = 1; /* arg */ \
548 while (va_arg(ap, char *)) { \
553 /* Copy varargs. */ \
554 char *args[count + 1 /* terminating NULL */]; \
555 args[0] = (char *)arg; /* there's no other way around the cast */ \
559 while ((x = va_arg(ap, char *))) { \
563 #define EXECL_COPY_VARARGS_END(args) \
565 #define EXECL_COPY_VARARGS(args) \
566 EXECL_COPY_VARARGS_START(args); \
567 EXECL_COPY_VARARGS_END(args);
569 int execl(char const *path, char const *arg, ...) {
570 EXECL_COPY_VARARGS(args);
572 /* execv() updates the environment. */
573 return execv(path, args);
575 int execlp(char const *file, char const *arg, ...) {
576 EXECL_COPY_VARARGS(args);
578 /* execvp() updates the environment. */
579 return execvp(file, args);
581 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
584 EXECL_COPY_VARARGS_START(args);
585 /* Get envp[] located after arguments. */
586 envp = va_arg(ap, char * const *);
587 EXECL_COPY_VARARGS_END(args);
589 /* execve() updates the environment. */
590 return execve(path, args, envp);
593 /* int execv(char const *, char * const []) */
594 HOOK_FUNC_DEF2(int, execv, char const *, path, char * const *, argv) {
595 DLSYM_FUNCTION(real_execv, "execv");
597 update_environment();
598 return real_execv(path, argv);
601 /* int execvp(char const *, char * const []) */
602 HOOK_FUNC_DEF2(int, execvp, char const *, file, char * const *, argv) {
603 DLSYM_FUNCTION(real_execvp, "execvp");
605 update_environment();
606 return real_execvp(file, argv);
610 extern char **environ;
611 int execvpe(char const *file, char * const argv[], char * const envp[]) {
612 /* Fake the environment so we can reuse execvp(). */
613 environ = (char **)envp;
615 /* execvp() updates the environment. */
616 return execvp(file, argv);